Direct injection spark ignition engines provide benefits over port injected spark ignition engine. For example, direct injection spark ignition engines may provide high levels of charge cooling so that they may operate with more spark advance and generate less NOx as compared to a similar port injected engine operating at similar speeds and loads. However, direct injection spark ignition engines may also generate more soot than a port injected engine at some engine operating conditions. For example, direct injection engines may generate greater amounts of soot at lower engine temperatures. The soot may be trapped in a particulate filter where it may be oxidized at a later time. However, some soot may pass through the particulate filter during conditions when the engine may be generating higher levels of soot. Therefore, it may be desirable to provide a way of limiting conditions where the engine may produce larger amounts of soot so that instances of higher soot flow through the particulate filter may be reduced.
The inventors herein have recognized the above-mentioned issues and have developed an engine operating method, comprising: adjusting an automatic engine stopping engine temperature threshold as a function of an amount of soot stored in a particulate filter via a controller; and automatically stopping an engine responsive to an engine temperature being greater than or equal to the automatic engine stopping engine temperature threshold.
By adjusting an automatic engine stopping engine temperature threshold as a function of an amount of soot stored in a particulate filter, it may be possible to provide the technical result of reducing soot flow through a particulate filter during conditions when an engine generates higher amounts of soot. In particular, if an amount of soot stored in a particulate filter is low, then the automatic engine stopping engine temperature threshold may be raised so that the engine may be automatically stopped only when engine temperature is relatively high. On the other hand, if the amount of soot stored in the particulate filter is high, then the automatic engine stopping engine temperature threshold may be reduced so that the engine may be automatically stopped at lower engine temperatures. The inventors herein have recognized that the efficiency of the particulate filter to trap soot increases as the amount of soot stored within the particulate filter increases. Therefore, an engine that includes a particulate filter that has trapped a threshold amount of soot may be stopped at lower temperatures without emitting higher levels of soot. This may allow engine fuel consumption to be reduced. If the same engine includes a particulate filter that has trapped less than a threshold amount of soot, the engine may not be automatically stopped until the engine has reached a higher temperature where the engine produces less soot so that engine emissions may be reduced.
The present description may provide several advantages. In particular, the approach may reduce engine soot emissions. Further, the approach may improve engine fuel efficiency by allowing the engine to be selectively deactivated. In addition, the approach may choose a type of fuel injection that conforms to the operating state of the particulate filter and engine emissions objectives so that engine emissions may be maintained at lower levels.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.